The present disclosure relates to the subject matter disclosed is German application No. 100 48 290.2 Sep. 29, 2000, which is incorporated herein by reference in its entirety and for all purposes.
The invention relates to an inductive sensor comprising at least one sensor coil in the form of a structured conductive layer of a carrier board, and an evaluation circuit which comprises a printed circuit board with conductor tracks provided thereon and is connected to the sensor coil.
Such inductive sensors are known from the prior art.
Herein the sensor coil is a separate component provided with flexible lines, and these lines have then to be connected to the printed circuit board of the evaluation circuit. To assemble the sensor coil and the evaluation circuit in a housing, the sensor coil and the evaluation circuit are placed separately by themselves or are introduced as a precast unit into the housing.
The object underlying the invention is, therefore, to so improve an inductive sensor of the generic kind that it is manufacturable in as cost-efficient a way as possible.
This object is accomplished with an inductive sensor of the kind described at the outset, in accordance with the invention, in that the carrier board carrying the sensor coil is mechanically rigidly and electrically connected to the printed circuit board by at least two soldered joints.
The advantage of the inventive solution is to be seen in the fact that two soldered joints are adequate to not only connect the sensor coil electrically to the printed circuit board, but to also simultaneously establish a mechanical connection between sensor coil and printed circuit board, so that the sensor coil and the printed circuit board form a unit for joint handling and insertion in the course of the further manufacturing process into the housing.
Such a solution offers considerable cost advantages for the manufacture, as there is no longer any need for flexible lines to be individually handled and soldered or for sensor coil and printed circuit board to be mechanically positioned, but instead an electrical connection can also be made simultaneously by two mechanically rigid soldered joints.
One type of design of the connection of carrier board and printed circuit board provides for one of the soldered joints to comprise a solder finger protruding from one of the boards and a solder surface arranged on the other board, with solder finger and solder surface being joined by a conventional solder aggregation.
It is even more advantageous for both soldered joints to comprise a solder finger protruding from one of the boards and a solder surface provided on the other board.
The advantage of providing a solder finger on one of the boards is that a solder finger can usually be arranged in a simple way, for example, by pressing it into one of the boards, and can also be easily brought into electrical contact with an electrically conductive layer of the board by this pressing-in.
Moreover, such a solder finger is rigid in itself, and this thus also results in a simple way in the inventive mechanically rigid soldered joint between the carrier board and the printed circuit board.
Such a solder finger can, for example, be in the form of a pin. It is, however, also conceivable for this solder finger to be in the form of a piece of flat material.
As an alternative to provision of solder fingers for the soldered joints, a further advantageous embodiment makes provision for one of the soldered joints to comprise two solder surfaces connected to each other by solder, one of which is arranged on one of the boards. This solution is particularly simple to implement as the solder surfaces can be created in a simple way by electrically conductive layers provided on the respective board, and thus merely the solder, for example, in the form of a solder aggregation, mechanically rigidly connects a solder surface on the printed circuit board with a solder surface of the carrier board.
It is thus possible to arrange the carrier board and the printed circuit board spatially in the desired orientation relative to each other and merely by applying a solder aggregation, thereby wetting the solder surfaces, to obtain a mechanically rigid connection between the carrier board and the printed circuit board after hardening of the solder aggregation.
It is particularly advantageous for each of the at least two soldered joints to comprise two solder surfaces connected to each other by solder, one of which is arranged on one of the boards.
The rigid connection is preferably achieved in a simple way by a single soldering operation, for example, by means of a solder bath, into which the carrier board and the printed circuit board dip in the desired orientation relative to each other, whereby both solder surfaces are automatically wetted, and the solder aggregation holding between the two on account of the wetting ensures the mechanically rigid connection between the carrier board and the printed circuit board after cooling of the solder aggregation.
A solder aggregation connecting the solder surfaces is achievable in a particularly reliable way by arranging the boards relative to each other in such a way that the solder surfaces essentially border on one another.
The solder surfaces are preferably arranged such that one of the solder surfaces extends transversely to the other solder surface, so that the desired solder aggregation can form in a simple way between these by wetting of the two solder surfaces.
The fact that the solder surfaces extend transversely to each other includes all acute angles up to a right angle.
It is particularly expedient for the solder surfaces to extend at an approximate right angle to each other, as a particularly advantageous arrangement of the carrier board in relation to the printed circuit board is thereby achievable for conventional housing shapes, and, in addition, owing to the right angle a sufficiently stable joining of the two solder surfaces by the solder aggregation joined to these and a sufficiently large volume of the solder aggregation owing to formation of a type of meniscus between these two solder surfaces are achievable.
No further details of the arrangement of the soldered joints relative to the boards were given in the above explanation of the individual embodiments.
It is, for example, possible for one of the soldered joints to be arranged on one side of the boards and the other soldered joint on the opposite side of the board.
As an alternative to this, it is possible for the at least two soldered joints to be arranged on one side of the respective board, so that the at least two soldered joints can be made in a particularly simple way by the application of solder.
In order to improve the quality of the mechanical joint, in particular, in view of tensions occurring upon cooling of the solder, provision is preferably made for there to be associated with at least one soldered joint arranged on one side of the respective board a corresponding soldered joint on an opposite side of the board.
This solution has the advantage that a soldered joint has associated therewith a corresponding soldered joint on the opposite side of the board, so the forces occurring upon cooling of the solder can thus be compensated in a simple way, and, in addition, it is possible to make the mechanical joint more stable and the electrical connection more fail-safe.
Further details of the arrangement of the printed circuit board and the carrier board relative to each other were not given in connection with the preceding embodiments. It is, for example, conceivable to arrange printed circuit board and carrier board relative to each other with a space between them.
It is, however, particularly expedient for the printed circuit board and the carrier board to abut on one another, as a particularly stable mechanical joint can thus be made between the two, in particular, by the printed circuit board and the carrier board supporting one another owing to their abutment on one another.
To obtain advantageous geometrical conditions, provision is expediently made for the printed circuit board and the carrier board to extend transversely to each other in an area of contact.
It is particularly expedient for the printed circuit board and the carrier board to extend approximately perpendicularly to each other in the area of contact.
An arrangement of printed circuit board and carrier board relative to each other, which is expedient for the design of the sensor, makes provision for the printed circuit board to be arranged close to a plane of symmetry of the carrier board extending perpendicularly to the carrier board.
No further details of the design of printed circuit board and carrier board were given in the above explanation of the individual embodiments. In principle, the boards could be of curved design.
For reasons of simplification, it is particularly expedient for the printed circuit board to be designed as a substantially flat board.
Moreover, it is likewise expedient for the carrier board to also be designed as a substantially flat board.
No further details of the type of the evaluation circuits were given in connection with the embodiments explained above. It is, for example, conceivable to use simple evaluation circuits which operate without an additional inductor, namely only with the sensor coil.
To increase the sensitivity and, in particular, to be able to compensate the temperature dependence of the coils, it is particularly expedient for the evaluation circuit to comprise at least one reference coil as better results are achieved with such evaluation circuits.
In principle, such a reference coil could be of conventional design and connected, for example, via flexible lines to the evaluation circuit.
However, a particularly expedient solution makes provision for the reference coil to be formed by a structured, electrically conductive layer of the printed circuit board, so that the reference coil can also be manufactured when the printed circuit board is being manufactured.
A particularly expedient embodiment does, however, make provision for the reference coil to be integrated in the form of conductor tracks in the printed circuit board. This solution has the advantage that a complicated wiring of the reference coil to the evaluation circuit is no longer necessary since the reference coil is also operatively connected to the evaluation circuit merely by the equipping of the printed circuit board.
This is realizable in different embodiments. One embodiment makes provision for the printed circuit board to be provided with a reference coil arranged in the form of a structured layer on the printed circuit board. This solution is the simplest solution and enables mounting of the reference coil in the same way as the component connections on the printed circuit board.
Moreover, such a reference coil arranged as layer on the printed circuit board also has the advantage that it can be tuned, for example, by layer ablation, for example, by the layer being ablated by means of a laser.
Another advantageous embodiment makes provision for the reference coil to be integrated into an intermediate layer between an upper and a lower layer of the printed circuit board. Such an integration of the reference coil into an intermediate layer makes it possible to construct the printed circuit board with a smaller size, as the space required by the sensor coil is eliminated when it is integrated in an intermediate layer between the upper and lower layers of the printed circuit board, which, for example, can both be equipped with components.
A further embodiment of the evaluation circuit makes provision for a multilayer reference coil.
The sensor coil can be designed in very different ways. It is conceivable to arrange the sensor coil on a front side or a rear side of the carrier board or as intermediate layer of the carrier board, so that the sensor coil is protected by the layers lying on either side of the intermediate layer. It is, however, also conceivable for the sensor coil to be of multilayer design.
No further details of the arrangement and design of the sensor coil were given in the above explanation of the individual embodiments. It is, for example, conceivable for the sensor coil to likewise be provided with a ferrite element arranged on the carrier board.
It is also conceivable to arrange a screening element on the carrier board.
An embodiment of the inventive sensor is particularly expedient when the sensor coil is surrounded by a screening provided in the form of a structured layer on the carrier board.
Such a screening can, for example, be designed in the simplest case as a short-circuited winding enclosing the sensor coil azimuthally.
However, more complicated shapes of a screening in the form of a layer applied to the carrier board, which are adapted to the individual applications, are also realizable.
Another advantageous embodiment, in particular, an embodiment wherein the characteristics of the sensor coil are to be adaptable makes provision for a damping element for the sensor coil, comprising a structured, electrically conductive layer on the carrier board, to be arranged on the carrier board.
Such a solution has the great advantage that with such a damping element the characteristics of the sensor coil can also be adapted in a simple way by tuning to special conditions.
Such a damping element can be implemented in a particularly expedient way when it comprises an electrical resistor which is arranged on the carrier board and is, for example, also tunable in order to be able to vary the damping by the damping element.
Furthermore, in order to have as low a space requirement as possible, a particularly expedient solution makes provision for the carrier board to be provided with electrical components in addition to the sensor coil. Such electrical components could, for example, in the case of inductive sensors, be a capacitor which is associated with the sensor coil for formation of an oscillating circuit.
Such additional electronic components could be arranged on the front side of the carrier board. It is, however, particularly expedient for these to be arranged on a rear side of the carrier board facing away from the sensor coil, as the sensor coil can thus be arranged as closely as possible to a housing side.
Further features and advantages of the inventive solution are the subject of the following description and the appended drawings of several embodiments.